The objectives of the proposed research constitutes a continuation of investigations on the transport of calcium and other mineral ions across the epithelium of the intestine. Emphasis will be given to different aspects of the problems of vitamin D action. Specific aims are to: (a) determine the amino acid sequence of chick CaBP and its interactions, (b) investigate in detail alterations in phopholipid metabolism as related to 1,25(OH)2D3 action, (c) to study possible 1,25(OH)2D3-mediated changes in membrane fluidity and mobility of membrane components, (d) initiate studies on the use of epithelial cell lines to investigate aspects of 1,25(OH)2D3 action, (e) investigate the properties and characteristics of the ATP-dependent basal-lateral pump, (f) identify and investigate the properties and function of specific 1,25(OH)2D3-modulated proteins and lipids, (g) examine hormonal effects in a model in which chicks are given 1,25(OH)2D3 as their only source of vitamin D3, and (h) to determine possible alterations in calmodulin behavior in calcium, phosphorus and vitamin D3-deficiency.